The present invention relates to an information holding device, and more particularly to such a device capable of outputting stored information to an external device.
In the past, a device made of a liquid crystal having a smectic phase with a display function and an information holding function and a device made of a dielectric material such as PLZT have been known as the information holding devices. Hereinbelow, a liquid crystal device having the display function and the information holding function will be explained as an example of the information holding device.
The liquid crystal devices of various display principles including a liquid crystal having a nematic phase, a liquid crystal having a cholesteric phase or a liquid crystal having a smectic phase have been known. In those devices, orientations of liquid crystal, molecules are changed by an external field and the resulting change of an optical property is used to display the information.
As an example of such liquid crystal devices, a thermal writing type liquid crystal device disclosed in U.S. Pat. No. 3,796,999 "Locally Erasable Thermo-Optic Smectic Liquid Crystal Storage Displays" will be explained below.
In the disclosed device, transparent electrodes 13 and 14 are arranged on the inner surfaces of a pair of glass substrates 11 and 12 as shown in FIG. 1a, and the space between them is filled with a liquid crystal 15 having a smectic phase. A laser beam 16 emitted from an argon (Ar) laser or a yttrium-aluminum-garnet (YAG) laser is focused on the display panel through a lens 17 to heat the smectic liquid crystal 15 of an area 18 to be displayed, thereby rendering it an isotropic liquid crystal phase.
Then, the laser beam is removed to quickly cool the liquid crystal to the smectic phase. As a result, orientations of the liquid crystal molecules are disturbed and a region 19 which exhibits a strong scattering property is produced as shown in FIG. 1b. Since this scattered state persists stably, a desired image information can be stored.
Based on the display principle described above, the thermal writing type display device can write a desired image information on the liquid crystal elements by the scan and the modulation of the laser beam, and local erasure is attained by the application of an electric field. Thus, it is preferable as a display device, but it does not have a function to read out the stored image information or a function to output the information to an external device such as a computer and it is merely used as an input device of an image information signal.
The other known liquid crystal devices (e.g., U.S. Pat. No. 4,196,974) also have only the function of displaying the image and they are not used as the information output devices.